A study of former soldiers in the United States has indicated that differences in IQ may explain almost a quarter of the differences in mortality between people of higher and lower social classes.

It has long been accepted that social status affects mortality, with a particular influence on death from cardiovascular events such as strokes and heart attacks. Many of these differences have been ascribed to stress, to income, and to behavioural factors such as smoking and diet — but these cannot explain the whole gap in longevity between the highest socio-economic groups and the lowest ones.